Variable configurations of nfrp ru tone sets in wireless networks

ABSTRACT

A flexible NFRP procedure is proposed where the AP can adjust the granularity of the possible answers to a given question. The NFRP trigger frame includes a tone set configuration indication representative of a number of tone groups per RU tone set. The number of possible FEEDBACK_STATUS values consequently also varies, making it possible for the AP to poll the stations for more detailed feedback reports. A station determines which FEEDBACK_STATUS values are available, calculates its FEEDBACK_STATUS value and retrieves the corresponding subset of tone groups on which energy must be sent. Due to the multiples existing tone set configurations, the station also determines the tones forming the subset to be activated, based on the tone set configuration indication. The station can then properly send its feedback report response by activating (emitting energy on) the appropriate tunes and therefore the appropriate tone groups.

CROSS REFERENCE TO RELATED APPLICATION

This is a National Stage Application filed under 35 U.S.C. 371 ofInternational Application No. PCT/EP2020/068255 filed on Jun. 29, 2020,which claims the benefit under 35 U.S.C. § 119(a)-(d) of United KingdomPatent Application No. 1909634.6, filed on Jul. 4, 2019 and entitled“VARIABLE CONFIGURATIONS OF NFRP RU TONE SETS IN WIRELESS NETWORKS”. Theabove-cited patent applications are incorporated herein by reference intheir entireties.

FIELD OF THE INVENTION

The present invention relates generally to communication networks andmore specifically to wireless communication methods in a wirelessnetwork and corresponding communication devices, such as an access point(AP) and non-AP stations.

BACKGROUND OF THE INVENTION

The IEEE 802.11 (RTM) family of standards provides multi-user (MU)schemes to allow a single access point (AP) to schedule MUtransmissions, i.e. multiple simultaneous transmissions to or fromnon-AP stations or “nodes”, in the wireless network. This approachincreases bandwidth and decreases latency requirements compared tooriginal 802.11 networks.

MU downlink (DL) transmission is allowed where the AP performs multiplesimultaneous elementary transmissions, over so-called resource units(RUs), to various non-AP stations. As an example, the resource unitssplit a communication channel of the wireless network in the frequencydomain, based for instance on Orthogonal Frequency Division MultipleAccess (OFDMA) technique.

MU uplink (UL) transmissions are also allowed that are triggered by theAP. Various non-AP stations can simultaneously transmit to the AP overthe resource units forming the MU UL transmission. To control the MU ULtransmission by the non-AP stations, the AP sends a control frame, knownas a Trigger Frame (TF), which defines a plurality of resource units forthe non-AP stations.

Various variants of trigger frames exist depending on the nature ofinformation the non-AP stations can provide in response. The mainvariant is the basic trigger frame for the non-AP stations to send anydata they wish.

Some RUs may be allocated in a basic trigger frame to specific non-APstations using 16-bit Association IDentifiers (AIDs) assigned to themupon registration to the AP (so-called scheduled RUs). Others RUs (knownas random RUs) are available to the non-AP stations using acontention-based access scheme.

A variant trigger frame to the basic trigger frame is theNull-Data-Packet (NDP) Feedback Report Poll (NFRP) trigger frameimplementing the so-called Null-Data-Packet (NDP) Feedback Reportprocedure. This procedure allows the AP to collect feedback that is notchannel sounding from multiple non-AP stations in a more efficientmanner than with a basic trigger frame. The AP sends a NFRP Triggerframe to solicit NDP feedback report responses about buffered bytes frommany non-AP stations that are identified by a range of scheduled AIDs inthe NFRP Trigger frame. Each non-AP stations is assigned a RU tone setmade of two groups of tones. The NDP feedback report response from anon-AP station is a HE trigger-based (TB) feedback NDP transmitted oneither tone group depending on the value of the response. The NDPfeedback report response can take two possible response values: 0 (fortransmission of the HE TB NDP over the first group of tones) if thebuffered bytes are lower than a predefined threshold and 1 (fortransmission of the HE TB NDP over the second group of tones) if thebuffered bytes are above the predefined threshold.

The NFRP procedure is short compared to the duration of an ULtransmission triggered by a basic Trigger frame. The AP thus has a firstknowledge of the stations' needs at low time cost.

However, the AP usually needs more precise and detailed information onthese stations' needs to efficiently schedule them in MU UL operations.This more precise and detailed information may be obtained throughBuffer Status Reports (BSRs) sent by the stations in a solicited orunsolicited manner. To solicit such reports by polling the stations, theAP uses another variant of trigger frames, the so-called Buffer StatusReport Poll (BSRP) trigger frame which provides scheduled and/or randomRUs for BSR transmission.

The need of unsolicited or solicited BSRs, and thus of an additionalBSRP procedure, shows that the NFRP procedure is not fully satisfactory.

SUMMARY OF INVENTION

The present invention seeks to overcome some of the foregoing concerns.

In this context, the invention provides a communication method in awireless network, comprising the following steps at a (non-AP) station:

receiving, from an access point, AP, a null data packet, NDP, feedbackreport poll, NFRP, trigger frame, the NFRP trigger frame reserving aplurality of resource unit, RU, tone sets for NDP feedback reportresponses by stations,

retrieving, from the NFRP trigger frame, a tone set configurationindication representative of a number of one or more groups of tonesforming each of the RU tone sets, wherein one or more subsets of thegroups of tones in an activated state correspond to one or more possibleresponse values for the NDP feedback report responses, respectively,

determining a response value for a NDP feedback report response by thestation to the NFRP trigger frame based on the tone set configurationindication, and

sending the NDP feedback report response by activating the tone groupsof the subset corresponding to the determined response value, in aselected responding RU tone set.

Only the tone group or groups of the subset are activated by the sendingof energy to make it possible for the AP to discriminate between thevarious possible NDP feedback report responses.

Correspondingly, the invention provides a communication method in awireless network, comprising the following steps at an access point:

sending, to (non-AP) stations, a null data packet, NDP, feedback reportpoll, NFRP, trigger frame, the NFRP trigger frame reserving a pluralityof resource unit, RU, tone sets for NDP feedback report responses bystations, wherein the NFRP trigger frame includes a tone setconfiguration indication representative of a number of one or moregroups of tones forming each of the RU tone sets, wherein one or moresubsets of the groups of tones in an activated state correspond to oneor more possible response values for the NDP feedback report responses,respectively,

receiving at least one NDP feedback report response through activationby at least one responding station of the tone groups of one of thesubsets in a responding RU tone set, and

determining a response value for the NDP feedback report response basedon the subset corresponding to the activated tone groups in theresponding RU tone set.

Thanks to the tone set configuration indication, the AP can dynamicallyadapt the number of tone groups per responding TU tone set and therebyadapt the number of possible response values for the stations.Consequently, the AP can adapt the response granularity of the polling.

Advantageously, the AP can then obtain more detailed buffer informationfrom the stations without involving a subsequent Buffer Status Reportpolling (BSRP).

Correlatively, the invention also provides a communication device,either the AP or a non-AP station, comprising at least onemicroprocessor configured for carrying out the steps of any of the abovemethods.

Optional features of embodiments of the invention are defined in theappended claims. Some of these features are explained here below withreference to a method, while they can be transposed into devicefeatures.

In one embodiment, each tone group subset of a RU tone set is made of asingle group of tones from the groups of tones forming the RU tone sets.In that case, the number of possible response values for the NDPfeedback report responses is equal to the number of tone groups per RUtone set. This embodiment advantageously allows collisions to be easilydetected at RU tone set level, for instance when the AP receives NDPfeedback report responses on a plurality of subsets within the same RUtone set.

In a variant, at least one tone group subset of a RU tone set is made oftwo or more groups of tones from the groups of tones forming the RU tonesets. In other words, all combinations of groups of tones may becontemplated to form a higher number of subsets, hence a higher numberof possible response values. In that case, the number of possibleresponse values for the NDP feedback report responses may be related to2^(n) where n is the number of tone groups per RU tone set. This variantthus advantageously offers a higher number of possible response values.

In some embodiments, determining the response value for a NDP feedbackreport response includes determining a response value from a set ofpossible response values the number of which depends on the tone setconfiguration indication. Indeed, by adjusting the tone setconfiguration indication, the AP controls the granularity of theresponses from the non-AP stations.

In some embodiments, tone groups (preferably each one) of the groups oftones forming the responding RU tone set are associated with respectivetraffic access categories, ACs, from a group of traffic ACs, anddetermining a response value for the NDP feedback report responsecomprises:

for each traffic AC, selecting or not the tone group associated with thetraffic AC based on an AC-based criterion, e.g. whether the amount ofbuffered bytes for this AC is above a predefined threshold or not, and

selecting the response value corresponding to the subset formed of theselected tone groups. A correspondence table may match the variousresults of the AC-based criteria to the various subsets (i.e.configurations of tone groups to be activated to send the response).

This approach efficiently improves the conventional NFRP polling byallowing the non-AP stations to give details on each AC. Consequently,the AP can adapt subsequent exchanges with the non-AP stations, forinstance to give priority to non-AP stations having buffered data inhigh priority ACs.

In some embodiments, the possible response values for the NDP feedbackreport response are associated with respective ranges for a stationmeasurement (e.g. amount of buffered data), each range being defined bya different multiplying factor applied to the same threshold value. Forinstance, first range is made from 0 to THR (e.g. response value is 0),second range from THR to 2×THR (e.g. response value is 1), . . . , lastrange above N×THR (e.g. response value is N). The station thus selectsthe response value corresponding to the range to which its measurementbelongs. This approach makes it possible for the AP to dynamicallyadjust the granularity of the obtained detailed information on aspecific measurement from the stations, without a need to send rangedefinitions for all the ranges.

In one embodiment, the tone set configuration indication is included ina Reserved field of a User Info field of the NFRP trigger frameaccording to Draft 4.1 of IEEE 802.11ax. This approach keepsretro-compatibility because it keeps unchanged the other fieldscurrently used.

In a variant, the tone set configuration indication is included in aTrigger Dependent Common Info field of a Common Info field of the NFRPtrigger frame according to Draft 4.1 of IEEE 802.11ax.

In yet another variant, the tone set configuration indication is definedby a feedback type field in the NFRP trigger frame. This approach keepscompliance with the current format of the NFRP trigger frame as variousvalues for the 802.11ax Feedback Type field are available for newusages. For instance, feedback type field=1 may upgrade the conventionalfeedback type field=0 (polling of resource request according to theamount of buffered bytes) by defining more (e.g. 3) tone groups per RUtone set, and thus allowing the non-AP stations to be more precise ontheir resource needs (a higher number of buffered byte thresholds isused).

In some embodiments, the tone set configuration indication is a 2-bitfield in the NFRP trigger frame and the number of one or more groups oftones forming each of the RU tone sets is equal to the tone setconfiguration indication plus 1. This provides a good tradeoff betweensignaling cost and details in the NDP feedback report response. Ofcourse, 3-bit filed, 4-bit field or larger fields may be used, dependingon the needs (in particular the number of possible response values).

In one embodiment, each RU tone set (throughout a set of tone setconfigurations available) has a fixed number of tones and the tone setconfiguration indication adjusts the number of tones per group. In thatcase, the tone set configuration indication may merely indicate thenumber of tones per group, thereby defining the number of groups per RUtone set. Consequently, the number of RU tone sets is fixed per 20 MHzchannel (without considering the MIMO spatiality) and their constitutingtones are split into the appropriate number of tone groups.Advantageously, this embodiment does not impact the number of stationsthe AP can poll per each 20 MHz channel.

In a variant, each group of tones has a fixed number of tones and thetone set configuration indication adjusts the number of RU tone sets. Inthat case, the tone set configuration indication may merely indicate thenumber of RU tone sets per 20 MHz channel, thereby defining the numberof groups per RU tone set. Consequently, the number of RU tone setsvaries per 20 MHz channel. Advantageously, the AP sensitivity fordetection of the NDP feedback report responses remains unchanged.

In both cases, the tone set configuration indication may merely indicatethe number of groups per RU tone set.

Of course, more complicated schemes may be envisioned where both numberof tones per group and number of RU tone sets (per 20 MHz channel) areadjusted by the tone set configuration indication.

In some embodiments, the method further comprises, at the station,determining whether the station is polled (i.e. targeted) by the NFRPtrigger frame based on the retrieved tone set configuration indication.Indeed, as the number N_(STA) of RU tone sets may vary depending on thetone set configuration indication, the number of targeted non-APstations also varies. The non-AP station may for instance determinewhether its AID is included in range [StartingAID, StartingAID+N_(STA)]where StartingAID is an AID specified in the NFRP trigger frame.

In some embodiments, the method further comprises, at the station,determining tones forming the subset of tone groups to be activated,based on the retrieved tone set configuration indication. The determinedtones are activated by transmission of null data packets NDP (energy) tothe AP. Indeed, as various tone set configurations are available, thenon-AP station needs to retrieve the appropriate configuration and thenactivate the appropriate tones for transmission of the NDP feedbackreport response. The correspondences between constituting tones and toneset configurations may be stored in a table local to each station.

In some embodiments, the method further comprises, at the AP,determining a number of stations having newly registered to the AP, and

determining the tone set configuration indication based on thedetermined number of newly registered stations.

For instance, the AP may provide a tone set configuration indicationrepresentative of a high number of groups of tones when a low number ofnewly registered stations is determined, or provide a tone setconfiguration indication representative of a low number of groups oftones when a high number of newly registered stations is determined.

The AP thus dynamically adapts the number of tone groups per RU tone setdepending on the activity, to either obtain more detailed informationfrom few non-AP stations or obtain coarser information from a highnumber of non-AP stations.

In some embodiments, the method further comprises, at the AP:

receiving NDP feedback report responses from responding stations anddetermining corresponding response values,

selecting a subset of the responding stations based on the correspondingresponse values so determined, and

sending, to the stations, a subsequent trigger frame reserving aplurality of resource units scheduled for stations of the selectedsubset. For instance, if the feedback responses from the stations arerepresentative of an amount of stored data for various ACs, the AP mayprovide MU UL operation for those responding stations that have AC_VOdata. This AP behavior helps to improve network QoS.

In some embodiments, the method may further comprise, at the AP,sending, to the stations, a second NFRP trigger frame reserving aplurality of second RU tone sets for NDP feedback report responses bystations, wherein the second NFRP trigger frame includes a tone setconfiguration indication representative of a number of one or moregroups of tones forming each of the second RU tone sets that isdifferent from the number of tone groups forming each of the RU tone setof the other NFRP trigger frame.

Correspondingly, the method may further comprise, at the station,receiving, from the AP, a second NFRP trigger frame reserving aplurality of second RU tone sets for NDP feedback report responses bystations, wherein the second NFRP trigger frame includes a tone setconfiguration indication representative of a number of one or moregroups of tones forming each of the second RU tone sets that isdifferent from the number of tone groups forming each of the RU tone setof the other NFRP trigger frame.

This feature mirrors the dynamic adaptation by the AP of the number oftone groups per RU tone set.

Another aspect of the invention relates to a non-transitorycomputer-readable medium storing a program which, when executed by amicroprocessor or computer system in a communication device, causes thecommunication device to perform any method as defined above.

The non-transitory computer-readable medium may have features andadvantages that are analogous to those set out above and below inrelation to the communication methods and devices.

At least parts of the methods according to the invention may be computerimplemented. Accordingly, the present invention may take the form of anentirely hardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit”, “module” or “system”. Furthermore,the present invention may take the form of a computer program productembodied in any tangible medium of expression having computer usableprogram code embodied in the medium.

Since the present invention can be implemented in software, the presentinvention can be embodied as computer readable code for provision to aprogrammable apparatus on any suitable carrier medium. A tangiblecarrier medium may comprise a storage medium such as a hard disk drive,a magnetic tape device or a solid-state memory device and the like. Atransient carrier medium may include a signal such as an electricalsignal, an electronic signal, an optical signal, an acoustic signal, amagnetic signal or an electromagnetic signal, e.g. a microwave or RFsignal.

BRIEF DESCRIPTION OF THE DRAWINGS

Further advantages of the present invention will become apparent tothose skilled in the art upon examination of the drawings and detaileddescription. Embodiments of the invention will now be described, by wayof example only, and with reference to the following drawings.

FIG. 1 illustrates a communication system in which embodiments of theinvention may be implemented;

FIG. 2 illustrates three usages of trigger frames; FIGS. 2a and 2billustrate, using flowcharts, corresponding general steps at the accesspoint and at a non-AP station, respectively;

FIG. 3a illustrates the format of a trigger frame, in particular of NFRPtype;

FIG. 3b illustrates the format of TB NDP PPDU;

FIG. 4 shows a schematic representation a communication device inaccordance with embodiments of the present invention;

FIG. 5 schematically illustrates functional blocks of a communicationdevice in accordance with embodiments of the present invention;

FIG. 6 illustrates embodiments of the invention providing variablenumber of tone groups (and thus of possible NFRP response values) per RUtone set during the NDP short feedback report procedure;

FIGS. 6a and 6b illustrate, using flowcharts, corresponding generalsteps at the access point and at a non-AP station, respectively; and

FIG. 7 illustrates an exemplary signaling of a tone set configuration ina NFRP trigger frame according to embodiments of the invention.

DETAILED DESCRIPTION

The invention will now be described by means of specific non-limitingexemplary embodiments and by reference to the figures.

In the description, the term legacy refers to non-802.11ax stations,meaning 802.11 stations of previous technologies that do not supportOFDMA communications.

FIG. 1 illustrates a communication system in which several communicationstations (or “nodes”) 101-107 exchange data frames over a radiotransmission channel 100 of a wireless local area network (WLAN), underthe management of a central station, or access point (AP) 110, also seenas a station of the network. The radio transmission channel 100 isdefined by an operating frequency band constituted by a single channelor a plurality of channels forming a composite channel.

In the following, the word “station” refers to any kind of station. Thewording “access point station”, or in short “access point” (AP), refersto the station playing the role of access point 110. The wording“non-access point station”, or in short “non-AP station”, or clientstation (STA) refers to the other stations 101-107. In the following,the terms HE STA and HE AP refer respectively to an 802.11ax non-AP STAand an 802.11ax AP.

Access to the shared radio medium to send data frames is primarily basedon the CSMA/CA technique, for sensing the carrier and avoiding collisionby separating concurrent transmissions in space and time.

Carrier sensing in CSMA/CA is performed by both physical and virtualmechanisms. Virtual carrier sensing is achieved by transmitting controlframes to reserve the medium prior to transmission of data frames.

Next, a source or transmitting station, including the AP, first attemptsthrough the physical mechanism, to sense a medium that has been idle forat least one DIFS (standing for

DCF InterFrame Spacing) time period, before transmitting data frames.

However, if it is sensed that the shared radio medium is busy during theDIFS period, the source station continues to wait until the radio mediumbecomes idle.

The wireless communication system of FIG. 1 comprises physical accesspoint 110 configured to manage the WLAN BSS (Basic Service Set), i.e. agroup of non-AP stations which have previously registered to the AP. Aphysical access point 110 may be configured to manage two or more WLANs(or BSSs), i.e. two or more groups of station. Each BSS is uniquelyidentified by a specific basic service set identifier, BSSID, andmanaged by a virtual AP implemented in the physical AP. po To access themedium, any station, including the AP, starts counting down a backoffcounter designed to expire after a number of timeslots when the mediumis sensed as idle. The backoff counter is chosen randomly in a so-calledcontention window [0, CW], where CW is an integer. This backoffmechanism or procedure, also referred to as Distributed CoordinationFunction (DCF) contention-based channel access scheme, is the basis ofthe collision avoidance mechanism that defers the transmission time fora random interval, thus reducing the probability of collisions on theshared channel. After the backoff time expires (i.e. the backoff counterreaches zero), the source station may send data or control frames if themedium is still idle. po Conventional single-user (SU) transmission canoccur on at least a primary 20 MHz channel (used for contention) andsome secondary 20 Mhz channels: The resulting bandwidth of an operatingchannel may be e.g. 20 MHz, 40 MHz, 80 MHz, 80+80 MHz, or 160+160 MHz,or 320 MHz. The channels may include one or more subcarriers or tones,for instance a 20 MHz channel is made of 242 tones. po Management ofquality of service (QoS) has been introduced at station level in thewireless networks, through well-known EDCA mechanism defined in the IEEE802.11e standard. EDCA (Enhanced Distributed Channel Access) mechanismdefines four traffic access categories (ACs) or «priorities» to manageaccess to the medium: a voice access category (AC_VO), a video accesscategory (AC_VI), a best effort access category (AC_BE) for standardapplications and a background access category (AC_BK) when traffic islow.

Developments in the 802.11ax standard seek to enhance efficiency andusage of the wireless channel for dense environments.

In this perspective, multi-user (MU) transmission features have beenconsidered that allow multiple simultaneous transmissions to/fromdifferent non-AP stations in both downlink (DL) and uplink (UL)directions from/to the access point. In the uplink, multi-usertransmissions can be used to mitigate the collision probability byallowing multiple non-AP stations to simultaneously transmit to the AP.

To actually perform such multi-user transmission, it has been proposedto split a legacy 20 MHz channel into at least one subchannel, butpreferably a plurality of sub-channels (elementary sub-channels), alsoreferred to as sub-carriers or resource units (RUs) or “trafficchannels”, that are shared in the frequency domain by multiple users,based for instance on Orthogonal Frequency Division Multiple Access(OFDMA) technique. In some embodiments, the bandwidth of the RUs may bebased on a number of active data subcarriers. In some embodiments, thebandwidth of the RUs is based on 26, 52, 106, 242 (a whole 20 MHzchannel), 484 (40MHz channel), 996 (80 MHz channel), or 2×996 (80+80 Mhzor 160 Mhz channel) active data subcarriers or “tones”.

While the MU DL transmission is fully managed by the AP, the MU ULtransmission requires the AP sends a control frame to the non-AP stationto trigger the simultaneous MU UL transmissions from the non-APstations. Such control frame is known as a Trigger Frame (TF), variousvariants of which exist depending on the usage of the MU UL sub-carriersdesired by the AP.

FIG. 2 illustrates two usages of trigger frames. In the exemplaryembodiment shown, a short feedback report procedure according to802.11ax (as described in section “26.5.7 NDP feedback report procedure”of Draft D4.1 of IEEE 802.11 ax) is shown followed by a Buffer StatusReport operation (as described in section “26.5.5 Buffer status reportoperation” of Draft D4.1 of IEEE802.11ax) based on the results of theshort feedback report procedure. A subsequent MU UL operation is theninitiated by the AP.

The NDP feedback report procedure allows the AP 110 to collect feedbackthat is not channel sounding from multiple non-AP STAs 101-107. The APsends an NFRP Trigger frame to solicit NDP feedback report response frommany non-AP STAs that are identified by a range of scheduled AIDs in theNFRP Trigger frame. A non-AP STA uses the information carried in theNFRP Trigger frame to know if it is scheduled, and in this case, maysend a NDP feedback report response, usually a HE TB feedback NDP.

Next, based on the received NDP feedback report responses, the AP maysolicit any responding non-AP STA, for instance solicit simultaneousimmediate response frames from one or more of the responding non-AP STAsusing a basic Trigger Frame (for UL MU operation) or a BSRP TriggerFrame as shown in the example.

The example shown considers a single 20 MHz channel. Of course, thebandwidth of the channel and the number of RUs splitting a 20 MHzchannel may be different from what is depicted. FIGS. 2a and 2billustrate, using flowcharts, corresponding general steps at the AP anda non-AP STA, respectively.

The AP is willing to poll non-AP stations using a feedback shortprocedure. At preliminary step S259, the AP determines NFRP parametersvalues for NFRP trigger frame 200 to be sent. NFRP trigger frame 200 isa specific trigger frame. It identifies the polled non-AP STAs by arange of scheduled AIDs.

With reference to FIG. 3a , like each and every 802.11ax trigger frame,NFRP trigger frame 200 comprises:

a frame header with a standardized “Frame Control” field, a standardized“Duration” field, an “RA” field set to a broadcast MAC address, and a“TA” field set to a MAC address of the AP transmitting the triggerframe,

a “Common Info” field 310,

one or more “User Info” fields 350, and

padding and FCS fields.

The “Common Info” field 310 comprises a “Trigger Type” subfield 320which specifies the type of the trigger frame. For instance, NFRPtrigger frame 200 is signaled by a value 7 in the “Trigger Type”subfield 320. It also comprises a 2-bit “UL BW” field 330 specifying thebandwidth of the channel considered, e.g. BW=0 to define a 20 MHzbandwidth, BW=1 for a 40 MHz bandwidth, BW=2 for an 80 MHz bandwidth,BW=3 for an 80+80 MHz or 160 MHz bandwidth (see Table 9-31c of the D4.1version of 802.11ax). It ends by a Trigger Dependent

Common Info subfield 340 of variable length whose content depends on the“Trigger Type” subfield 320. The other fields shown are of lessimportance for the present invention.

Specific to the trigger frame of NFRP type, a single “User Info” field350 is provided that comprises a 12-bit Starting AID field 351, a firstreserved 9-bit portion 352, a 4-bit feedback type field 353, a secondreserved 7-bit portion 354, a 7-bit UL Target RSSI field 355 and a 1-bitmultiplexing flag field 356.

The Starting AID comprises the starting AID of the range of AIDstargeted by the NFRP trigger frame 200, i.e. scheduled to respond to thepoll. The range size or width N_(STA) is defined by the “UL BW” field330 together the 1-bit multiplexing flag field 356, using the followingformula

N _(STA)=18×2^(BW)×(MultiplexingFlag+1)

For instance, when the MultiplexingFlag is set to 0 (no MIMO), 18 non-APSTAs are requested to answer with a feedback response, per 20 MHzoperating channel. When the MultiplexingFlag is set to 1, 36 non-AP STAsare scheduled per 20 MHz operating channel. It may be noted that someAIDs in the 18 or 36-wide range may not be currently assigned to anon-AP STA.

The multiplexing flag field 356 defines whether spatiality (MIMO) isprovided: the flag indicates the number (minus 1) of non-AP STAs thatare multiplexed on the same set of tones in the same RU.

The “feedback type” field 353 indicates a type of feedback that is beingpolled by the AP. For the time being, 802.11ax D4.1 only defines afeedback type equal to 0 that is a resource request. The correspondingpolling thus seeks to know whether the responding non-AP STAs 101-107are requesting UL resources to transmit PPDUs to the AP 110.

At step S259, the AP thus determines the values for StartingAID field351, Feedback Type field 353, Multiplexing Flag field 356 and UL BWfield 330.

At phase 199, the AP 110 accesses the wireless medium. For example, theAP performs a contention-based method (which may include a clear channelassessment and an EDCA backoff) to acquire access to the wirelessmedium.

Upon accessing the medium, the AP 110 polls non-AP STAs to know theirneeds for transmission. To do so, it sends NFRP trigger frame 200 atstep S260.

In the example of FIG. 2, the NFRP trigger frame 200 is sent in a 20 MHzprimary channel. However, as already discussed, the NFRP trigger frame200 may also be sent through an extended channel such as 40 MHz, 80 MHzor larger bands to extend the number of polled stations. By sendingtrigger frame 200, the AP reserves a transmission opportunity 260 (TXOP)corresponding to the duration specified inside the NFRP trigger frame.

If the NFRP trigger frame is sent over an overall width larger than theprimary 20 MHz channel, the 802.11ax standard envisages that the NFRPtrigger frame is duplicated (replicated) on each other 20 MHz channelsforming the targeted composite channel. Thanks to the duplication ofcontrol-type frames in non-HT format, it is expected that every nearbylegacy node (non-HT or 802.11ac nodes) receiving the NFRP trigger frame(or a duplicate thereof) on its primary channel, then sets its NAV tothe value specified in the NFRP trigger frame. This prevents theselegacy nodes from accessing the channels of the targeted compositechannel during the TXOP.

Each non-AP STA receiving frame 200 is able to first analyze thereceived frame 200 to determine whether the non-AP STA is concerned withit, in particular to determine whether the non-AP STA is associated withthe BSSID indicated in the TA field of the frame (or if the indicatedBSSID pertains to a multiple BSSID set for which the non-AP STA ismember of).

In case of positive determination, it then determines whether receivedframe 200 is a NFRP trigger frame, thanks to the type specified inTrigger Type field 320. These determinations form step S270 (FIG. 2b ).

Next, the non-AP STA determines whether it is scheduled or “polled” bythe received NFRP trigger frame (step S272). It is made by checkingwhether its AID value (assigned to the non-AP STA by the AP uponregistration to the AP) falls within the range [“Starting AID”;“Starting AID”+N_(STA)] as obtained from the fields UL BW 330, StartingAID 351 and Multiplexing flag 356 of the received NFRP trigger frame200.

When the non-AP STA is not scheduled, nothing more happens at the non-APstation.

If it is polled by the NFRP trigger frame, the scheduled non-AP STAdetermines a RU tone set index, i.e. a RU tone set 210 on which thenon-AP STA will transmit energy in response to the NFRP trigger frame.This is step S274. The non-AP STA usually selects a responding RU toneset based on the position of its AID within the above range, meaning thefirst RU tone set for the non-AP station having the Starting AID as ownAID, and so on.

Table 27-30 of 802.11ax D4.1 describes an example of how the tonesforming 80 MHz, 40 MHz, 20 MHz channels are grouped into sets of tones.

For instance, 216 tones (indexed from −113 to −6 and 6 to 113) forming a20 MHz channel are split into six bundles 250 of 36 continuous tones.Next each RU tone set is formed by two tones from each bundle (usuallyconsecutive tones that are collocated from one bundle to the other),thereby resulting in 18 RU tone sets, each having a unique indexRU_TONE_SET_INDEX. The two tones obtained from each bundle are assignedto two respective groups forming the RU tone set. It means that each RUtone set is formed of two groups of tones 210 a and 210 b.

For illustrative purposes, the tone set with RU_TONE_SET_INDEX=6 in a 20MHz channel without spatiality is made of the two following groups oftones (subcarrier indices):

Group 210 a: −103, −67, −31, 16, 52, 88

Group 210 b: −102, −66, −30, 17, 53, 89

In this example, 6 tones are replicated in each group over the 20 MHzchannel, each tone from one of the six bundles of tones 250.

A RU tone set is thus made of two adjacent groups of tones (−103 isadjacent to −102, −67 to −66 and so on.), each group being made ofnon-adjacent tones (−103 not adjacent to −67 and so on.).

Basically, the tone set index for the scheduled non-AP STA is computedfrom the difference between STA's AID value and “Starting AID” value(usually the difference plus 1). For instance, if this difference plus 1equals 6, the above-detailed tone set having RU_TONE_SET_INDEX=6 isscheduled for the non-AP STA considered.

Next at step S276, the non-AP STA generates the NDP feedback reportresponse to be sent to the AP.

In particular, the non-AP STA has to transmit energy on the first group210 a of subcarriers or tones to indicate a first response to thefeedback type (field 353) polled by the NFRP trigger frame 200, and onthe other hand, the non-AP STA must transmit energy on the second group210 b of subcarriers or tones to indicate a second response to thefeedback type. The encoding of the response is thus performed byactivating (i.e. sending energy) the corresponding group of tones.

The response is named FEEDBACK_STATUS in the current D4.1 version of802.11ax. For instance, for the Feedback Type field 353 set to 0(Resource request),

FEEDBACK_STATUS is set to 0 when the non-AP STA requests resource withbuffered bytes for transmission between 1 and a resource request bufferthreshold. The non-AP station will thus use (i.e. activate) the firstgroup 210 a of tones;

FEEDBACK_STATUS is set to 1 when the non-AP STA requests resource withbuffered bytes for transmission above the resource request bufferthreshold. The non-AP station will thus use (i.e. activate) the secondgroup 210 b of tones.

The non-AP station determines the NDP feedback report response to besent depending on the feedback type field in the NFRP trigger frame.

Table 27-30 of 802.11 ax D4.1 specifies which group of tones within atone set has to be used depending on the FEEDBACK_STATUS value. At stepS276, the non-AP STA thus determines the FEEDBACK_STATUS value andtherefore the group of tones to be used, either 210 a or 210 b,depending on the feedback it wishes to report to the AP.

Next at step S278, the non-AP STA transmits energy on the groupcorresponding to the FEEDBACK_STATUS value in the RU tone set of thedetermined RU_TONE_SET_INDEX.

For illustration, Station 1 (corresponding to RU_TONE_SET_INDEX=1)transmits energy on its first group of tones 210 a (as consequence,group 210 b is represented with a dash line), thereby activating thelatter. On the contrary, Station 2 (corresponding toRU_TONE_SET_INDEX=1) transmits energy on its second group of tones 210b, thereby activating the tones of this second group.

Technically, the HE TB NDP Feedback PPDU 211 used as a feedback responseis a single packet with no real data payload as shown in FIG. 3b . ThePHY preamble 212 is emitted on 20 MHz width (thus several non-AP STAsmay emit the same preamble) and the ‘payload’ is composed of a series ofHE-LTF symbols 213, located on the tones forming the selected group 210a or 210 b, to be used for the transmitted feedback (energy).

Then, the physical layer of the AP receives and decodes (S262) the RUtone sets where energy is present, to provide its MAC layer with a listof used RU_TONE_SET_INDEX and the corresponding Feedback responses(FEEDBACK_STATUS values).

Thanks to the fields UL BW 330, Starting AID 351 and Multiplexing flag356 of the NFRP trigger frame 200 sent at step S260, the AP is able toretrieve the AID of each responding RU tone set with energy, and therebyretrieve the AID of each non-AP STA responding to the trigger frame 200.The MAC layer entity of the AP is consequently able to determine thoseNDP-scheduled non-AP STAs who have responded.

At step S264, the AP can send a subsequent trigger frame 220 (FIG. 2) tooffer new opportunities (RUs) to the responding non-AP STAs, for examplea ‘Basic’ type trigger frame to let the non-AP stations send any type ofdata or a ‘BSRP’ type trigger frame (as shown in the example) to receiveBSRs from the non-AP stations or any convenient type. The ‘Basic’ typetrigger frame is signaled by a “Trigger Type” subfield 320 having value0 while the ‘BSR’ type trigger frame is signaled by a “Trigger Type”subfield 320 having value 4.

Based on an AP's decision and the collected feedback responses 211, thetrigger frame 220 may define a plurality of data resource units (RUs)230 (here of 26 tones—of course other numbers of tones may be used). Themulti-user feature of OFDMA allows the AP to assign different RUs todifferent non-AP STAs in order to increase competition. This helps toreduce contention and collisions inside 802.11 networks.

These RUs may be scheduled RUs assigned to the feedback-respondingnon-AP STAs, using the AIDs retrieved at step S264.

The trigger frame 220 may for instance include a plurality of User Infofields (FIG. 3a ) for a respective plurality of scheduled RUs, each UserInfo field setting an AID (so-called AID12 field) of the schedulednon-AP STA for a given RU in the channel.

The non-AP STAs thus receive the subsequent trigger frame 220 anddetermine whether they are scheduled (step S280).

In the affirmative, the non-AP STA can use the RU scheduled to it (i.e.the one with the AID corresponding to the non-AP STA) and transmit data(HE TB PPDU) to the AP, in the example a QOS_Null frame with BSR as thetrigger frame 220 is of BSRP type.

According to the exemplary illustration, Station 1 and Station 4 canthus be granted a RU 230. As an example, Station 1 emits a QoS_Null withBuffer Status Report 231 (the HE TB PPDU is a MAC-PDU with no datapayload but with a MAC header containing a BSR) in a first RU 230-1, andStation 4 emits a QoS_Null with Buffer Status Report 231 in a second RU230-2.

Upon receiving the HE TB PPDU 231, the AP acknowledges (or not) the dataon each RU by sending a multi-STA block acknowledgment (BA) response(240—FIG. 2), making it possible for each sending non-AP STA to knowwhen its data transmission is successful (reception of the ACK) or not(no ACK after expiry of a time-out). This is step S266.

It is then possible for the AP to provides other opportunities (RUs) forthe non-AP stations whose BSR indicates some buffered data are to besent. A Basic Trigger Frame 220′ may for instance be sent by the AP toprovide subsequent UL MU operation with RUs scheduled for thesestations.

These explanations show the intent of the NFRP trigger frame mechanismaccording to the current version of the 802.11ax standard: to receivefeedbacks in a short time from a high number of associated non-APstations.

The overall MU Uplink (UL) medium access sequence, including both NDPFeedback RUs and BSRP or UL MU scheduled RUs, seems more efficient thanconventional EDCA access scheme, especially in dense environments asenvisaged by the 802.11ax standard. This is because the number ofcollisions generated by simultaneous medium access attempts and theoverhead due to the medium access are both reduced. The NFRP triggerframe 200 allows information to be requested from 18 non-AP stations per20 MHz channel (more with spatial multiplexing), and the NFRP or Basictrigger frame 220/220′ allows RUs to be proposed to up to 9 stationswhich have shown their interest to be triggered (by responding to theNFRP trigger frame).

In this exemplary scenario, the non-AP stations first signal theirinterest to be triggered using the short feedback procedure, then the APpolls the responding non-AP stations to know details on their needs orthe AP hopes to receive unsolicited BSRs from the non-AP stations,otherwise the AP could only trigger a very basic UL MU operation that isbadly tuned to stations' needs. This is because the short feedbackprocedure only allows the non-AP stations to provide a binary responserepresentative of whether it has more or less buffered bytes than athreshold.

Only when all the detailed needs are known by the AP through the BSRPprocedure, the latter can trigger an efficient UL MU operation targetingthe non-AP stations with specific needs.

However, the addition of the Null-Data-Packet (NDP) Feedback Reportprocedure and the BSRP procedure is bandwidth and time consuming.

The inventors have thus contemplated providing a more flexible NFRPfeedback report procedure, allowing the AP to adjust the granularity ofthe possible answers to a given question, while keeping the NFRPadvantages such as a large number of non-AP stations polled and lowlatency.

In this perspective, the proposed invention provides a NFRP triggerframe that includes a tone set configuration indication representativeof a number of one or more groups of tones forming each of the RU tonesets, and one or more subsets of the groups of tones in an activatedstate (i.e. if energy is sent on them) correspond to one or morepossible response values for the NDP feedback report responses,respectively. By adjusting the number of tone groups per RU tone set,the AP adjusts the number of possible NDP responses and hence thedetails the non-AP stations can transmit to the AP regarding a givenfeedback type (i.e. a question).

A non-AP station having a NFRP response value to be sent thus determinesthe subset of tone groups corresponding to the NFRP response value giventhe tone set configuration corresponding to the tone set configurationindication. This ensures the non-AP station to send its NDP feedbackreport response by activating the appropriate tone group subset (forappropriate understanding by the AP), i.e. the one corresponding to thedetermined response value given the tone set configuration indication.The group or groups of tones to be activated to send the response canthus change for a given response value, because the tone setconfiguration changes depending on the indication provided by the AP.

Consequently, the AP can decide when it wishes to receive more detailedinformation, e.g. a precise amount of buffered bytes, to efficientlyschedule a subsequent UL MU operation, or when it wishes to receivecoarser information to poll a higher number of non-AP stations.

FIG. 4 schematically illustrates a communication device 400 of the radionetwork 100, either the AP 110 or any non-AP STA 101-107, configured toimplement at least one embodiment of the present invention. Thecommunication device 400 may preferably be a device such as amicro-computer, a workstation or a light portable device. Thecommunication device 400 comprises a communication bus 413 to whichthere are preferably connected:

-   -   a central processing unit 411, such as a microprocessor, denoted        CPU;    -   a read only memory 407, denoted ROM, for storing computer        programs for implementing the invention;    -   a random-access memory 412, denoted RAM, for storing the        executable code of methods according to embodiments of the        invention as well as the registers adapted to record variables        and parameters necessary for implementing methods according to        embodiments of the invention; and    -   at least one communication interface 402 connected to the radio        communication network 100 over which digital data packets or        frames or control frames are transmitted, for example a wireless        communication network according to the 802.11ax/be protocols.        The frames are written from a FIFO sending memory in RAM 412 to        the network interface for transmission or are read from the        network interface for reception and writing into a FIFO        receiving memory in RAM 412 under the control of a software        application running in the CPU 411.

Optionally, the communication device 400 may also include the followingcomponents:

-   -   a data storage means 404 such as a hard disk, for storing        computer programs for implementing methods according to one or        more embodiments of the invention;    -   a disk drive 405 for a disk 406, the disk drive being adapted to        read data from the disk 406 or to write data onto said disk;    -   a screen 409 for displaying decoded data and/or serving as a        graphical interface with the user, by means of a keyboard 410 or        any other pointing means.

The communication device 400 may be optionally connected to variousperipherals, such as for example a digital camera 408, each beingconnected to an input/output card (not shown) so as to supply data tothe communication device 400.

Preferably the communication bus provides communication andinteroperability between the various elements included in thecommunication device 400 or connected to it. The representation of thebus is not limitative and in particular the central processing unit isoperable to communicate instructions to any element of the communicationdevice 400 directly or by means of another element of the communicationdevice 400.

The disk 406 may optionally be replaced by any information medium suchas for example a compact disk (CD-ROM), rewritable or not, a ZIP disk, aUSB key or a memory card and, in general terms, by an informationstorage means that can be read by a microcomputer or by amicroprocessor, integrated or not into the apparatus, possibly removableand adapted to store one or more programs whose execution enables amethod according to embodiments of the invention to be implemented.

The executable code may optionally be stored either in read only memory407, on the hard disk 404 or on a removable digital medium such as forexample a disk 406 as described previously. According to an optionalvariant, the executable code of the programs can be received by means ofthe communication network 403, via the interface 402, in order to bestored in one of the storage means of the communication device 400, suchas the hard disk 404, before being executed.

The central processing unit 411 is preferably adapted to control anddirect the execution of the instructions or portions of software code ofthe program or programs according to the invention, which instructionsare stored in one of the aforementioned storage means. On powering up,the program or programs that are stored in a non-volatile memory, forexample on the hard disk 404 or in the read only memory 407, aretransferred into the random access memory 412, which then contains theexecutable code of the program or programs, as well as registers forstoring the variables and parameters necessary for implementing theinvention.

In a preferred embodiment, the apparatus is a programmable apparatuswhich uses software to implement the invention. However, alternatively,the present invention may be implemented in hardware (for example, inthe form of an Application Specific Integrated Circuit or ASIC).

FIG. 5 is a block diagram schematically illustrating the architecture ofthe communication device 400 adapted to carry out, at least partially,the invention. As illustrated, communication device 400 comprises aphysical (PHY) layer block 503, a MAC layer block 502, and anapplication layer block 501.

The PHY layer block 503 (e.g. a 802.11 standardized PHY layer) has thetask of formatting, modulating on or demodulating from any 20 MHzchannel or the composite channel, and thus sending or receiving framesover the radio medium used 100, such as 802.11 frames, for instancesingle-user frames, such as control frames (e.g. ACK, Trigger Frame),MAC data and management frames, based on a 20 MHz width to interact withlegacy 802.11 stations or with 802.11ax/be in legacy mode (such as forTrigger Frames), as well as MAC data frames of OFDMA type havingpreferably smaller width than 20 MHz legacy (typically 2 or 5 MHz), aswell as NDP frames having preferably a PHY header transmitted on 20 MHzwidth and a short payload consisting on energy located on non-contiguoussubcarriers or tones, to/from that radio medium.

The MAC layer block or controller 502 preferably comprises a MAC 802.11layer 504 implementing conventional 802.11ax/be MAC operations, and anadditional block 505 for carrying out, at least partially, embodimentsof the invention. The MAC layer block 502 may optionally be implementedin software, which software is loaded into RAM 412 and executed by CPU411.

Preferably, the additional block 505 referred to as NDP FeedbackManagement module 505 is configured to implement steps according toembodiments that are performed by the communication device 400, notablytransmitting operations for a transmitting/responding station andreceiving operations for a receiving station.

Interfaces 506 and 507 are used by the MAC and PHY layer blocks tointeract and to exchange information through TXVECTOR (from the MAC tothe PHY layer—506) and the RXVECTOR (from the PHY to the MAC block—507).The TXVECTOR and RXVECTOR are defined in the clause 27.2.2 of the draft4.1 of the 802.11ax standard.

On top of the Figure, application layer block 501 runs an applicationthat generates and receives data packets, for example data packets of avideo stream. Application layer block 501 represents all the stacklayers above MAC layer according to ISO standardization. Embodiments ofthe present invention are now illustrated using various exemplaryembodiments.

Although some of the proposed examples use the trigger frames 200 and220′ (see FIG. 2) sent by an AP for a multi-user (MU) uplink (UL)transmissions, equivalent mechanisms can be used in a centralized or inan ad hoc environment (i.e. without an AP). It means that the operationsdescribed below with reference to the AP may be performed by any stationin an ad hoc environment. In particular, subsequent scheduling toprovide scheduled transmission opportunities to the NFRP respondingnon-AP stations may be provided that is different from the 802.11ax ULMU operation.

FIG. 6 illustrates embodiments of the invention providing variablenumber of tone groups (and thus of possible NFRP response values) per RUtone set during NDP short feedback report procedures. FIGS. 6a and 6billustrate, using flowcharts, corresponding general steps at the AP anda non-AP STA, respectively. The reference numbers are unchanged whenreferring to the same elements, frames and steps as in FIGS. 2.

The AP is willing to poll non-AP stations using a feedback shortprocedure in order to provide UL MU operation.

At step S659, the AP 110 determines NFRP parameters values for NFRPtrigger frame 600 to be sent. According to the invention, this includesdetermining a RU tone set configuration for the NDP feedback reportresponses.

Each RU tone set configuration defines a number N_(feedback) of RU tonesets per 20 MHz channel (no MIMO considered at this level), a numberN_(TG) of tone groups per RU tone set and a number N_(tones) of tonesper tone group. In fact, these three numbers are linked by the followingformula N_(feedback)×N_(tones)×N_(TG)=number of tones per 20 MHz channel(216 in 802.11ax D4.1). Therefore, the knowledge of two of these numbersis enough.

In some embodiments, the number N_(feedback) of RU tone sets 610 per 20MHz channel is kept unchanged (e.g. 18 sets) through the configurationsmeaning that each RU tone set 210 has a fixed number of tones, namely 12tones per RU tone set. In that case, the number N_(tones) of tones pergroup varies from one configuration to the other when offering differentnumbers N_(TG) of tone groups 610 a, 610 b, 610 c per RU tone set. Inthese embodiments, the total number N_(STA) of RU tone sets remainsunchanged: N_(STA)=N_(feedback)×2^(BW)×(MultiplexingFlag+1) whereN_(feedback) is fixed.

A first illustrative configuration with N_(TG)=2 splits the 12 tones ofa RU tone set into two tone groups 210 a, 210 b, thereby having 6 tonesper group (N_(tones)=6). This is the configuration known from 802.11ax(see FIG. 2).

A second configuration with N_(TG)=3 splits the 12 tones of a RU toneset into three tone groups 610 a-c, thereby having 4 tones per group(N_(tones)=4). This may correspond to the configuration partly shown inthe first short feedback procedure of FIG. 6 (provided that they are 18RU tone sets 610, only two of which are shown).

Other configurations may provide 3 tones per group (N_(TG)=4), 2 tonesper group (N_(TG)=6), 1 tone per group (N_(TG)=12) or 12 tones per group(N_(TG)=1).

In other embodiments, the number N_(tones) of tones per group is keptunchanged through the configurations meaning that each group of tones610 a-c has a fixed number of tones, e.g. 6 tones per group as proposedin 802.11 ax D4.1. In that case, the number N_(feedback) of RU tone sets610 varies from one configuration to the other when offering differentnumbers N_(TG) of tone groups 610 a-c per RU tone set. It turns thatN_(STA)=N_(feedback)×2^(BW)×(MultiplexingFlag+1) where N_(feedback)varies.

A first illustrative configuration with N_(TG)=2 uses 12 tones per RUtone set 210 and provides 18 RU tone sets for a 20 MHz channel (242tones but only 216 tones available for RU tone sets). This is theconfiguration known from 802.11ax (see FIG. 2).

A second configuration with N_(TG)=3 uses 18 tones per RU tone set 610and thus provides 12 RU tone sets for a 20 MHz channel. This maycorrespond to the configuration partly shown in the first short feedbackprocedure of FIG. 6 (provided that they are 12 RU tone sets 610, onlytwo of which are shown).

Other configurations may provide 9 RU tone sets per 20 MHz channel(N_(TG)=4), 6 RU tone sets per 20 MHz channel (N_(TG)=6), 4 RU tone setsper 20 MHz channel (N_(TG)=9), 3 RU tone sets per 20 MHz channel(N_(TG)=12), 2 RU tone sets per 20 MHz channel (N_(TG)=18), or 36 RUtone sets per 20 MHz channel (N_(TG)=1). Of course, other approaches mayprovide a set of tone set configurations in which both numbersN_(feedback) and N_(tones) vary. In particular, the set ofconfigurations may for instance comprises two or more configurationscorresponding to the same number N_(TG) of tone groups per RU tone set,but with different numbers N_(feedback) and N_(tones). Theconfigurations are linked so that N_(feedback)×N_(tones)×N_(TG)=numberof tones per 20 MHz channel (here 216). For illustrative purposes,configurations with N_(TG)=4 may be such that N_(feedback)×N_(tones)=54,e.g.:

N_(feedback)=18 and N_(tones)=3,

N_(feedback)=9 and N_(tones)=6,

N_(feedback)=6 and N_(tones)=9, and so on.

The various configurations available to the AP and the non-AP stationsare known from them, for instance stored in tables in local memory. Eachconfiguration may be assigned a unique identifier ID_(config).Therefore, each configuration identifier ID_(config) is representativeof a number N_(TG) of one or more groups of tones forming each of the RUtone sets.

As mentioned previously, the tone groups 610 a-c of the RU tone sets 610are used to encode the FEEDBACK_STATUS value forming NDP feedback reportresponse, because the non-AP stations send energy (NDP feedback PPDU211) on the tone groups corresponding to the FEEDBACK_STATUS. Inparticular, subsets of the groups of tones in an activated state (i.e.on which the non-AP stations will emit energy) correspond to possibleresponse values for the NDP feedback report response, respectively. Thenumber MAX_ENCODED_VALUE of possible FEEDBACK_STATUS values thus dependson the varying number N_(TG) of tone groups per RU tone set, and henceon the configuration identifier ID_(config) chosen by the AP.

It may be decided that each FEEDBACK_STATUS value is associated withonly one respective tone group 610 a-c, meaning that only one tone groupis generally activated at a time (i.e. energy is sent by a station ononly one tone group of a responding RU tone set). Therefore, N_(TG)FEEDBACK_STATUS values are possible to respond. In other words, thenumber MAX_ENCODED_VALUE of possible response values for the NDPfeedback report responses is equal to the number of tone group subsetsper RU tone set. In that case, the non-AP stations will use a tone groupsubset to send their NDP feedback report responses, that is made of asingle group of tones from the groups of tones forming the RU tone sets.

In a variant, a subset made of two or more groups of tones maycorrespond to a possible response value, meaning that two or more tonegroups are activated at the same time (i.e. energy is sent on aplurality of tone groups of a responding RU tone set). In that case, thenumber MAX_ENCODED_VALUE of possible response values for the NDPfeedback report responses is increased. It is related to 2^(n) where nis the number N_(TG) of tone groups 610 a-c per RU tone set 610.

Since any NDP feedback report response requires that energy be sent onat least one tone group 610 a-c, the maximum number forMAX_ENCODED_VALUE is 2^(n)−1.

In some embodiments, the binary encoding for the FEEDBACK_STATUS mayrequire that there must be at least one “1” (energy on a tone group) andone “0” (no energy on a tone group). This may be to allow the ADC,Analog to Digital Converter, to determine the two values by measuringthe min and max power level measured on the tones of a tone set. In thatcase, the response value using all or none of the tone groups isforbidden, and therefore the maximum number for MAX_ENCODED_VALUE is2^(n)−2. Consequently, the number of possible response values is in therange [0, MAX_ENCODED_VALUE] with MAX_ENCODED_VALUE equal to 1 forN_(TG)=0, to 2 for N_(TG)=1, to 6 to N_(TG)=3, to 14 for N_(TG)=4, andso on.

Given the tone set configurations available, the AP has to decide on thegranularity of the NDP feedback report responses, i.e. on theMAX_ENCODED_VALUE value it wishes and thus on N_(TG).

Furthermore, the AP can decide on the number N_(STA) of RU tone sets itwishes to offer to the non-AP stations:N_(STA)=N_(feedback)×2^(BW)×(MultiplexingFlag+1). Where N_(feedback) isfixed, the AP can only adjust BW and Multiplexing flag values.Otherwise, it also determines N_(feedback).

Such decisions performed at step S659 makes it possible for the AP todetermine the most appropriate tone set configuration to be used. Bydefault, N_(TG) may be set to 2 in order to select the tone setconfiguration corresponding to Table 27-30 of 802.11ax D4.1. This valuemay evolve over time as the AP evaluates network behavior (includingnumber of non-AP stations, etc.).

For instance, the AP may select a tone set configuration representativeof a high number N_(TG) of groups of tones depending on the number ofnew non-AP stations having recently (e.g. since the last short feedbackprocedure) registered to the AP. Indeed, the AP already knows little ormore about already registered non-AP stations but needs to know aboutnew non-AP stations' needs to correctly serve then.

Consequently, when the number of new non-AP stations is reduced, less RUtone sets may be offered with a higher number N_(TG) of tone groups perRU tone set, hence the AP can request a more precise evaluation of thebuffered data ready for transmission in the queues of the polled non-APstations.

On the other hand, when the number of new non-AP stations is high, theAP may wish to obtain coarse or rough evaluation of the buffered dataamount for a high number of these stations. In other words, more RU tonesets may be offered with a lower number N_(TG) of tone groups per RUtone set.

Consequently, the AP may determine a number of stations having newlyregistered to the AP, e.g. since a previous NFRP trigger frame orprevious NFRP procedure, and then determine the tone set configurationbased on the determined number of newly registered stations (for thenext NFRP procedure).

At this stage, the AP knows the tone set configuration it wishes to usefor the RU tone sets of the forthcoming short feedback procedure. Thetone set configuration is uniquely identified by its ID_(config).

N_(feedback), N_(tones) and N_(TG) are known.

The AP also determines the other NFRP parameters such as:

BW 330 and Multiplexing Flag 356, depending on the number of non-APstations the AP wishes to poll (or number of RU tone sets the AP wishedto offer to the non-AP stations),

Feedback type 353, depending on the question the AP wishes to ask to thepolled non-AP stations, and

StartingAID 351, depending on which range of AIDs the AP wishes to poll.In a variant to scheduled AIDs where StartingAID defines the first AIDof the polling range, the NFRP trigger frame may offer random RU tonesets that the non-AP stations can access using contention. A signalingof such random-based RU tone sets may be provided by setting StartingAIDto a predefined value known by all stations, e.g. to 0 to target all thenon-AP stations yet associated with the AP, or to a Basic Service SetIdentifier, BSSID, index of a BSS to poll all the non-AP stationsbelonging to this BSS, or to any other value that targets a specificgroup of non-AP stations.

In the example of FIG. 6, the AP has thus decided to use a tone setconfiguration with three tone groups 610 a-c per RU tone set 610(N_(TG)=3).

Next, at step S660, the AP builds the NFRP trigger frame 600 and sendsit to poll non-AP STAs to know their needs for transmission.

The tone set configuration selected at step S659 is specified in theNFRP trigger frame 600.

Various way to signal it may be envisioned.

In some embodiments, ID_(config) is encoded using a x-bit field(referred below to as “RU configuration field”), where integer x is suchas 2^(x) is the ceiling of the number of tone set configurationsavailable less 1, e.g. the number of possible values for N_(TG) less 1when the set of tone set configurations comprises only one tone setconfiguration per N_(TG) value.

For easy of illustration, ID_(config) may be set to N_(TG)−1 when N_(TG)can take the values 1, 2, 3 and 4 thereby requiring a 2-bit field:

ID_(config) in RU configuration N_(TG) - number of tone groups per fieldRU tone set 0 (binary 00) 1 1 (binary 01) 2 2 (binary 10) 3 3 (binary11) 4

In one embodiment, the x-bit RU configuration field 3520 is included inReserved field 352 or 354 as illustrated in FIG. 7 for instance.

In a variant, the x-bit RU configuration field is included in TriggerDependent Common Info field 340.

In other embodiments, the Feedback Type (field 353) may indicatesimultaneously both the question to be answered by the non-AP stationsduring the short feedback procedure and the tone set configuration to beused for the RU tone sets. The Feedback Type thus acts as an ID_(config)indication.

802.11ax D4.1 currently defines Feedback Type=0 for resource requestusing two tone groups 210 a, 210 b per RU tone set 210. Other values ofthe Feedback Type may be used still for resource request but using adifferent number N_(TG) of tone groups per RU tone set. Thisadvantageously keeps retrocompatibility with the current version of802.11ax. For instance,

Feedback Type 353 N_(TG) - number of tone groups per (ID_(config)) RUtone set 0 2 (conventional scheme) 1 1 2 3 3 4

Of course, other allocations of Feedback Types with N_(TG) values may becontemplated. More generally, any correspondence between the FeedbackTypes and the ID_(config) may be provided (to allow various tone setconfigurations having the same N_(TG)).

At step S270, any non-AP station 101-107 receives the NFRP Trigger frame600 and decodes it. If the receiving non-AP station belongs to a BSS (orvirtual BSS) of the transmitting AP, the Trigger Frame is not filteredby the PHY layer as defined in the standard.

The filtering is made on so-called “colors” defined in the 802.11axstandard, which mandates that the BSS colors of all the multiple BSSsmanaged by a single AP are the same.

At step S671, the non-AP STA retrieves the tone set configurationindication from the NFRP trigger frame 600, for instance theconfiguration identifier ID_(config) from RU Configuration field (e.g.3520).

At step S672, the non-AP STA determines whether it is polled (i.e.targeted) by the NFRP trigger frame 600.

In case the NFRP trigger frame 600 provides random RU tone sets(StartingAID 351 set to 0 or BSSID index or any suitable value), thenon-AP station can determine whether it belongs to the targeted group ofAIDs, and in the affirmative, then determine by its own whether it hasinterest in contending for access to the random RU tone sets. In theaffirmative, the test S672 is positive.

In case the NFRP trigger frame 600 defines a polling range [StartingAID,StartingAID+N_(STA)], the determination is based on the retrieved toneset configuration and the conventional NFRP parameters, because varioustone set configurations are available and target a varying number ofnon-AP stations.

The non-AP station thus obtains N_(feedback) from the retrieved tone setconfiguration (the parameters of which being stored in a local table)and then calculates N_(STA)=N_(feedback)×2^(BW)×(MultiplexingFlag+1).

When the number N_(tones) of tones per tone group is fixed (e.g. 6 as in802.11ax D4.1), this formula becomesN_(STA)=(36/N_(TG))×2^(BW)×(MultiplexingFlag+1)=(36/(ID_(config)+1))×2^(BW)×(MultiplexingFlag+1).

In the example of FIG. 6, N_(TG)=3. Consequently, N_(STA)=12 (for a 20MHz channel without MIMO). The polling range is thus [StartingAID,StartingAID+12].

The non-AP stations thus checks whether its AID is included in thepolling range. If the STA's AID is higher (or equal) to Starting AID 351and lower than the sum of Starting AID 351 and N_(STA) value sodetermined, then the non-AP station is addressed by the current NFRPtrigger frame.

At step S674, the non-AP STA determines the index RU_TONE_SET_INDEX ofthe RU tone set 610 to be used to transmit energy in response to theNFRP trigger frame.

In case of random RU tone sets, the selection of the RU tone set is madeon a random basis, by randomly selecting an index from among theavailable indexes. All the RU tone sets are available for contention.Optionally, only the RU tone sets that fit into station capabilities areeligible for contention (e.g. a station operating on a limited band BWsuch as a 20 MHz-only station). The non-AP STA therefore randomlyselects a RU tone set Index to send its short feedback:RU_TONE_SET_INDEX=random [0, N_(STA)−1]. Here, it is chosen to start theindexes at 0. In variant, the first index may have another value, e.g. 1or above, and the provided formulae are modified accordingly.

In case of scheduled RU tone sets, the scheduled non-AP STA usuallyselects a responding RU tone set based on the position of its AID withinthe above polling range, meaning the first RU tone set for the non-APstation having the Starting AID as own AID, the second RU tone set forthe non-AP station having the next AID in the polling range, and so on.

In other words, the non-AP stations selects RU_TONE_SET_INDEXcorresponding to its AID minus StartingAID.

Next at step S676, the non-AP station determining a response value (i.e.FEEDBACK_STATUS value) for NDP feedback report response to the NFRPtrigger frame 600, based on the tone set configuration retrieved at stepS671. It is also based on the station's internal status (e.g. an amountof buffered data). Indeed, for instance, the same amount of bufferedbytes may correspond to different FEEDBACK_STATUS values depending onthe response granularity (i.e. N_(TG)) imposed by the AP.

As mentioned above, N_(TG) values may be available for theFEEDBACK_STATUS when each response value corresponds to only one and thesame tone group. In a variant, 2{circumflex over ( )}N_(TG)−1 or2{circumflex over ( )}N_(TG)−2 values may be available when the tonegroups may be combined. This maximum value is referred to asMAX_ENCODED_VALUE.

The possible response values for FEEDBACK_STATUS may be associated withrespective ranges for a station measurement corresponding to theFeedback Type (e.g. amount of buffered data). Therefore,FEEDBACK_STATUS=0 corresponds to a first measurement range,FEEDBACK_STATUS=1 corresponds to a next measurement range, and so on.Each range may be defined by a different multiplying factor applied tothe same threshold value TH. For instance the first measurement rangemay be [0; TH[, the second measurement range [TH; 2.TH[, and so on (thelast measurement range being from MAX_ENCODED_VALUE.TH).

When applied to the buffered bytes, the possible FEEDBACK_STATUSresponse can be based on a multiple of the queue size threshold asdefined in FIG. 2. In this case, FEEDBACK_STATUS is set to the maximumvalue n satisfying Q (amount of buffered data)≥n×TH, with n in [0,MAX_ENCODED_VALUE]. This embodiment is compatible with current 802.11axD4.1 approach where only 2 responses are possible: 1 if Q>1×TH, 0otherwise (Q>0×TH).

In other embodiments, the FEEDBACK_STATUS values may be used to reportthe amount of buffered data per each EDCA access category, AC. Forinstance, a tone set configuration with four tone groups per RU tone setmakes it possible to give feedback for each of the four EDCA ACs.

A Feedback Type (field 353) different from 0 may be used to request suchfeedbacks per AC. The AP can thus switch between requesting report ofthe overall amount of buffered data with respect to a threshold value(conventional scheme with N_(TG)=2) and requesting report of thepresence of buffered data per each AC with respect to the thresholdvalue.

Preferably, N_(TG)=4, in which case a tone group is assigned to a firstAC (e.g. AC_VO), a second group to a second AC (AC_VI), a third group toa third AC (AC_BE) and a fourth group to a fourth AC (AC_BK). If theamount of buffered data for a given AC is above the threshold, thenon-AP station selects the corresponding tone group. All the selectedtone groups form a subset of tone groups to be activated (by sendingenergy). The FEEDBACK_STATUS is chosen to correspond to the subset (i.e.to send energy on all the selected tone groups). Indeed, all theselected tone groups will be activated, and the AP, detecting energy onthem, will directly know which ACs have buffered bytes above thethreshold.

Once the response value for the FEEDBACK_STATUS is known, the non-APstation sends the NDP feedback report response over the selectedresponding RU tone set (i.e. with RU_TONE_SET_INDEX) at step S678. Thesending consists in activating the appropriate tone groups 610 a-c, i.e.sending energy (HE TB NDP Feedback PPDU 211) on them.

Based on the retrieved tone set configuration, the non-AP stationdetermines the tone indices forming the tone groups for theFEEDBACK_STATUS. This may be done by retrieving the tone mapping for theHE TB feedback NDP, given the tone set configuration used. Table 27-30of 802.11ax D4.1 gives an example of such tone mapping that isapplicable for N_(TG)=2. Similar mappings may be stored locally for allthe possible tone set configurations (mappings known by all thestations, including the AP).

The table below provides an illustrative excerpt of two tone mappingsfor some RU_TONE_SET_INDEX (1 to 4) and for two tone set configurationscorresponding to N_(TG)=2 and N_(TG)=3, when N_(tones)=6:

N_(TG) = 2 (802.11 ax D4.1) N_(TG) = 3 1^(st) tone 2^(nd) tone 1^(st)tone 2^(nd) tone 3^(rd) tone RU_TONE_SET_INDEX group (210a) group (210b)group (610a) group (610b) group (610c) 1 −113, −77, −41, −112, −76, −40,−113, −77, −41, −112, −76, −40, −111, −75, −39, 6, 42, 78 7, 43, 79 6,42, 78 7, 43, 79 8, 44, 80 2 −111, −75, −39, −110, −74, −38, −110, −74,−38, −109, −73, −37, −108, −72, −36, 8, 44, 80 9, 45, 81 9, 45, 81 10,46, 82 11, 47, 83 3 −109, −73, −37, −108, −72, −36, −107, −71, −35,−106, −70, −34, −105, −69, −33, 10, 46, 82 11, 47, 83 12, 48, 84 13, 49,85 14, 50, 86 4 −107, −71, −35, −106, −70, −34, −104, −68, −32, −103,−67, −31, −102, −66, −30, 12, 48, 84 13, 49, 85 15, 51, 87 16, 52, 8817, 53, 89 and so on.

In this example, each RU tone set is thus made of adjacent groups oftones (−113 is adjacent to −112, itself adjacent to −111 [for N_(TG)=3],−77 to −76 which is adjacent to −75, and so on.), each group being madeof non-adjacent tones (−113 not adjacent to −77 and so on.).

Once the tone indices for FEEDBACK_STATUS are known, the non-AP stationsends the HE TB NDP Feedback PPDU 211 on them.

The non-AP STA transmits the header 212 of TB Feedback PPDU 211 on the20 MHz channel corresponding to the selected RU_TONE_SET_INDEX, andtransmits on each of the subcarrier indexes determined for theFEEDBACK_STATUS value, the value of the HE-LTF sequence 213.

In the example of FIG. 6, Station 1 transmits energy (NDP) on tone group610 a of its responding RU tone set (index=1) for instance to indicateit has an amount of buffered bytes between 0 and TH, while Station 2transmits energy (NDP) on tone group 610 b of its responding RU tone set(index=2) for instance to indicate it has an amount of buffered bytesbetween TH and 2.TH. The third tone group 610 c could be used by anynon-AP station to report an amount of buffered data above 2.TH.

As explained above, the value of FEEDBACK_STATUS can also lead a non-APstations to transmit energy (NDP) on several tone group 610 a-c at thesame time. For instance, with N_(TG)=4 a non-AP station may transmitenergy (NDP) on the first and third tone groups from amongst the fourtone groups available, to indicate it has buffered bytes for AC_VO andAC_BE.

The AP receives and decodes (S262) the RU tone sets where energy ispresent, to provide to its MAC layer a list of used RU_TONE_SET_INDEXand the corresponding Feedback responses (FEEDBACK_STATUS values). Atthis stage, the AP knows the transmission needs of the polled stations.

In case random RU tone sets were provided, it is not possible for the APto know exactly which non-AP stations has responded on which RU toneset.

At step S664, the AP can send a subsequent trigger frame 220′ to offernew opportunities (RUs) to the responding non-AP STAs, for example a‘Basic’ type trigger frame or any convenient type. Preferably, thescheduled RUs are of narrow width (26 tones) to offer a maximum of nineRUs per 20 MHz channel. The AP may select a subset of the respondingnon-AP STAs, preferably based on the NFRP responses received. Forinstance, the AP may offer RUs to those responding non-AP stationshaving a large amount of buffered bytes or having buffered bytes inpriority ACs.

The AP thus retrieves the AIDs of the selected responding non-APstations, usually StartingAID+RU_TONE_SET_INDEX for those non-APstations having been scheduled in the short feedback procedure. Forthose non-AP stations having selected a responding RU tone set on arandom basis, the AP may use an AID based on the RU_TONE_SET_INDEX, forinstance RU_TONE_SET_INDEX+Offset_AID, where Offset_AID is 2048 orhigher to avoid any conflict with the AIDs conventionally assigned tothe non-AP stations by the AP.

At step S664, the AP 110 thus sends the subsequent basic trigger frame220′ so built.

Any non-AP STA receiving the subsequent trigger frame 220′ thusdetermines (step S680) whether it is scheduled, i.e. whether a resourceunit is assigned its own AID or to RU_TONE_SET_INDEX (selected at stepS674)+Offset_AID in case of random-based NFRP procedure.

In case of positive determination at step S680, the non-AP STA can usethe RU scheduled to it and transmit data 231 (HE TB PPDU) to the AP.This is step S282. The HE TB PPDU 231 contains the MAC address of thesending non-AP station, making it possible for the AP to identify eachsending non-AP station involved in a RU assigned toRU_TONE_SET_INDEX+Offset AID.

As shown in FIG. 6,

-   -   Station 1 has responded to the NFRP trigger frame 600 and has        been selected by the AP for the MU UL operation. It is then        allocated a scheduled RU 230-1 for transmission of its data;    -   Station 4 has also responded to the NFRP trigger frame 600 and        has been selected by the AP for the MU UL operation. It is then        allocated a scheduled RU 230-2 on which it transmits data.

The AP 110 thus receives the HE TB PPDU 231 over the multiple scheduledRUs. It can then acknowledge (or not) the data on each RU by sending amulti-STA block acknowledgment (BA) response 240, making it possible foreach sending non-AP STA to know when its data transmission is successful(reception of the ACK) or not (no ACK after expiry of a time-out). Thisis step S266.

The process may then loop back to S659 for the AP in order to send a newNFRP trigger frame 620 with another tone set configuration (N_(TG)=2 inthe example). The new NFRP trigger frame includes a tone setconfiguration indication representative of a number N_(TG)=2 of tonegroups per RU tone set that is different from the number N_(TG)=3 oftone groups used by the first NFRP trigger frame 600. Consequently, theAP 110 can dynamically adapt the configuration of the RU tone sets tonetwork conditions for instance.

Although the present invention has been described herein above withreference to specific embodiments, the present invention is not limitedto the specific embodiments, and modifications will be apparent to askilled person in the art which lie within the scope of the presentinvention.

Many further modifications and variations will suggest themselves tothose versed in the art upon referring to the foregoing illustrativeembodiments, which are given by way of example only and which are notintended to limit the scope of the invention, that being determinedsolely by the appended claims. In particular, the different featuresfrom different embodiments may be interchanged, where appropriate.

In the claims, the word “comprising” does not exclude other elements orsteps, and the indefinite article “a” or “an” does not exclude aplurality. The mere fact that different features are recited in mutuallydifferent dependent claims does not indicate that a combination of thesefeatures cannot be advantageously used.

1. A communication method in a wireless network, comprising thefollowing steps at a station: receiving, from an access point, AP, anull data packet, NDP, feedback report poll, NFRP, trigger frame, theNFRP trigger frame reserving a plurality of resource unit, RU, tone setsfor NDP feedback report responses by stations, retrieving, from the NFRPtrigger frame, a tone set configuration indication representative of anumber of one or more groups of tones forming each of the RU tone sets,wherein one or more subsets of the groups of tones in an activated statecorrespond to one or more possible response values for the NDP feedbackreport responses, respectively, determining a response value for a NDPfeedback report response by the station to the NFRP trigger frame basedon the tone set configuration indication, and sending the NDP feedbackreport response by activating the tone groups of the subsetcorresponding to the determined response value, in a selected respondingRU tone set.
 2. The method of claim 1, further comprising, at thestation, determining tones forming the subset of tone groups to beactivated, based on the retrieved tone set configuration indication. 3.The method of claim 1, further comprising, at the station, determiningwhether the station is polled by the NFRP trigger frame based on theretrieved tone set configuration indication.
 4. The method of claim 1,wherein determining the response value for a NDP feedback reportresponse includes determining a response value from a set of possibleresponse values the number of which depends on the tone setconfiguration indication.
 5. The method of claim 1, further comprising,at the station, receiving, from the AP, a second NFRP trigger framereserving a plurality of second RU tone sets for NDP feedback reportresponses by stations, wherein the second NFRP trigger frame includes atone set configuration indication representative of a number of one ormore groups of tones forming each of the second RU tone sets that isdifferent from the number of tone groups forming each of the RU tone setof the other NFRP trigger frame.
 6. The method of claim 1, wherein eachtone group of the groups of tones forming the responding RU tone set isassociated with a respective traffic access category, AC, from a groupof traffic ACs, and determining a response value for the NDP feedbackreport response comprises: for each traffic AC, selecting or not thetone group associated with the traffic AC based on an AC-basedcriterion, and selecting the response value corresponding to the subsetformed of the selected tone groups.
 7. A communication method in awireless network, comprising the following steps at an access point:sending, to stations, a null data packet, NDP, feedback report poll,NFRP, trigger frame, the NFRP trigger frame reserving a plurality ofresource unit, RU, tone sets for NDP feedback report responses bystations, wherein the NFRP trigger frame includes a tone setconfiguration indication representative of a number of one or moregroups of tones forming each of the RU tone sets, wherein one or moresubsets of the groups of tones in an activated state correspond to oneor more possible response values for the NDP feedback report responses,respectively, receiving at least one NDP feedback report responsethrough activation by at least one responding station of the tone groupsof one of the subsets in a responding RU tone set, and determining aresponse value for the NDP feedback report response based on the subsetcorresponding to the activated tone groups in the responding RU toneset.
 8. The method of claim 7, further comprising, at the AP,determining a number of stations having newly registered to the AP, anddetermining the tone set configuration indication based on thedetermined number of newly registered stations.
 9. The method of claim7, wherein the AP provides a tone set configuration indicationrepresentative of a high number of groups of tones when a low number ofnewly registered stations is determined, or provides a tone setconfiguration indication representative of a low number of groups oftones when a high number of newly registered stations is determined. 10.The method of claim 7, further comprising, at the AP: receiving NDPfeedback report responses from responding stations and determiningcorresponding response values, selecting a subset of the respondingstations based on the corresponding response values so determined, andsending, to the stations, a subsequent trigger frame reserving aplurality of resource units scheduled for stations of the selectedsubset.
 11. The method of claim 7, further comprising, at the AP,sending, to the stations, a second NFRP trigger frame reserving aplurality of second RU tone sets for NDP feedback report responses bystations, wherein the second NFRP trigger frame includes a tone setconfiguration indication representative of a number of one or moregroups of tones forming each of the second RU tone sets that isdifferent from the number of tone groups forming each of the RU tone setof the other NFRP trigger frame.
 12. The method of claim 1, wherein eachtone group subset of a RU tone set is made of a single group of tonesfrom the groups of tones forming the RU tone sets.
 13. The method ofclaim 1, wherein the number of possible response values for the NDPfeedback report responses is equal to the number of tone groups per RUtone set, or wherein the number of possible response values for the NDPfeedback report responses is related to 2^(n) where n is the number oftone groups per RU tone set.
 14. The method of claim 1, wherein at leastone tone group subset of a RU tone set is made of two or more groups oftones from the groups of tones forming the RU tone sets.
 15. The methodof claim 1, wherein the possible response values for the NDP feedbackreport response are associated with respective ranges for a stationmeasurement, each range being defined by a different multiplying factorapplied to the same threshold value.
 16. The method of claim 1, whereinthe tone set configuration indication is included in a Reserved field ofa User Info field of the NFRP trigger frame according to Draft 4.1 ofIEEE 802.11ax, wherein the tone set configuration indication is includedin a Trigger Dependent Common Info field of a Common Info field of theNFRP trigger frame according to Draft 4.1 of IEEE 802.11ax, wherein thetone set configuration indication is defined by a feedback type field inthe NFRP trigger frame, or wherein the tone set configuration indicationis a 2-bit field in the NFRP trigger frame and the number of one or moregroups of tones forming each of the RU tone sets is equal to the toneset configuration indication plus
 1. 17. The method of claim 1, whereineach RU tone set has a fixed number of tones and the tone setconfiguration indication adjusts the number of tones per group.
 18. Themethod of claim 1, wherein each group of tones has a fixed number oftones and the tone set configuration indication adjusts the number of RUtone sets.
 19. A non-transitory computer-readable medium storing aprogram which, when executed by a microprocessor or computer system in acommunication device, causes the communication device to perform thecommunication method of claim
 1. 20. A communication device comprisingat least one microprocessor configured for carrying out the steps of thecommunication method of claim
 1. 21. A non-transitory computer-readablemedium storing a program which, when executed by a microprocessor orcomputer system in a communication device, causes the communicationdevice to perform the communication method of claim
 7. 22. Acommunication device comprising at least one microprocessor configuredfor carrying out the steps of the communication method of claim 7.